在我的Android应用程序中

dependencies {
    ...
    implementation "com.android.billingclient:billing:6.0.0"
}

在build.gradle和

import androidx.annotation.NonNull;

在我的Java代码中。
如果我将计费版本更改为4.0.0，如下所示：

dependencies {
    ...
    implementation "com.android.billingclient:billing:4.0.0"
}

我的Java代码停止编译，并得到以下错误：

error: cannot find symbol
import androidx.annotation.NonNull;
                          ^
  symbol:   class NonNull
  location: package androidx.annotation

如何解决这个问题？
我试着加上

implementation "androidx.annotation:annotation:1.6.0"

build.gradle，但它没有帮助。
在我的gradle.properties中，我有：

android.useAndroidX=true
android.enableJetifier=true

编辑1

我得到“java.lang.NullPointerException：尝试使用依赖于billing v6的新版本对空对象引用“”调用虚拟方法“boolean com.android.settingslib.media.MediaDevice.isConnected（）”：

Exception Process: com.android.settings, PID: 20342
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.android.settingslib.media.MediaDevice.isConnected()' on a null object reference
  at com.android.settingslib.media.MediaDevice.compareTo (MediaDevice.java:325)
  at com.android.settingslib.media.MediaDevice.compareTo (MediaDevice.java:56)
  at java.util.Comparators$NaturalOrderComparator.compare (Comparators.java:52)
  at java.util.Comparators$NaturalOrderComparator.compare (Comparators.java:47)
  at java.util.TimSort.countRunAndMakeAscending (TimSort.java:355)
  at java.util.TimSort.sort (TimSort.java:220)
  at java.util.Arrays.sort (Arrays.java:1492)
  at java.util.ArrayList.sort (ArrayList.java:1470)
  at java.util.Collections.sort (Collections.java:206)
  at com.android.settingslib.media.LocalMediaManager$MediaDeviceCallback.onDeviceListAdded (LocalMediaManager.java:484)
  at com.android.settingslib.media.MediaManager.dispatchDeviceListAdded (MediaManager.java:91)
  at com.android.settingslib.media.InfoMediaManager.refreshDevices (InfoMediaManager.java:407)
  at com.android.settingslib.media.InfoMediaManager.access$000 (InfoMediaManager.java:61)
  at com.android.settingslib.media.InfoMediaManager$RouterManagerCallback.onRoutesAdded (InfoMediaManager.java:514)
  at android.media.MediaRouter2Manager.lambda$notifyRoutesAdded$0 (MediaRouter2Manager.java:671)
  at android.media.MediaRouter2Manager$$ExternalSyntheticLambda6.run
  at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1167)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:641)
  at java.lang.Thread.run (Thread.java:920)